ym_java-javagjsrc.rar_java fso

//FileRandomRW.java //Download by http://www.codefans.net import java.io.*; import java.util.*; public class FileRandomRW { //需要输入的person数目。 public static int NUMBER = 3; public static void main(String[] args) { Person[] people = new Person[NUMBER]; people[0] = new Person("张三", 25, 3000); people[1] = new Person("李四", 35, 10000, "Y"); people[2] = new Person("王大五", 30, 4000, "F"); try { DataOutputStream out = new DataOutputStream(new FileOutputStream("peoplerandom.dat")); //将人员数据保存至“peoplerandom.dat”二进制文件中。 writeData(people, out); //关闭流。 out.close(); //从二进制文件“peoplerandom.dat”中逆序读取数据。 RandomAccessFile inOut = new RandomAccessFile("peoplerandom.dat", "rw"); Person[] inPeople = readDataReverse(inOut); //输出读入的数据。 System.out.println("原始数据："); for (int i = 0; i < inPeople.length; i++) System.out.println(inPeople[i]); //修改文件的第三条记录。 inPeople[2].setSalary(4500); //将修改结果写入文件。 inPeople[2].writeData(inOut, 3); //关闭流。 inOut.close(); //从文件中读入的第三条记录，并输出，以验证修改结果。 RandomAccessFile in = new RandomAccessFile("peoplerandom.dat", "r"); Person in3People = new Person(); //随机读第三条记录。 in3People.readData(in, 3); //关闭流。 in.close(); System.out.println("修改后的记录"); System.out.println(in3People); } catch(IOException exception) { System.err.println("IOException"); } } //将数据写入输出流。 static void writeData(Person[] p, DataOutputStream out) throws IOException { for (int i = 0; i < p.length; i++) p[i].writeData(out); } //将数据从输入流中逆序读出。 static Person[] readDataReverse(RandomAccessFile in) throws IOException { //获得记录数目。 int record_num = (int)(in.length()/Person.RECORD_LENGTH); Person[] p = new Person[record_num]; //逆序读取。 for (int i = record_num-1 ; i >= 0 ; i--) { p[i] = new Person(); //文件定位。 in.seek(i * Person.RECORD_LENGTH); p[i].readData(in, i+1); } return p; } } class Person { private String name; private int age; //4个字节 private double salary; //8个字节 private String married; public static final int NAME_LENGTH = 20; //姓名长度 public static final int MARRIED_LENGTH = 2;//婚否长度 public static final int RECORD_LENGTH = NAME_LENGTH * 2 + 4 + 8 + MARRIED_LENGTH * 2; public Person() { } public Person(String n, int a, double s) { name = n; age = a; salary = s; married = "F"; } public Person(String n, int a, double s, String m) { name = n; age = a; salary = s; married = m; } public String getName() { return name; } public int getAge() { return age; } public double getSalary() { return salary; } public String getMarried() { return married; } public String setName(String n) { name = n; return name; } public int setAge(int a) { age = a; return age; } public double setSalary(double s) { salary = s; return salary; } public String setMarried(String m) { married = m; return married; } //设置输出格式。 public String toString() { return getClass().getName() + "[name=" + name + ",age=" + age + ",salary=" + salary + ",married=" + married + "]"; } //写入一条固定长度的记录，即一个人的数据到输出流。 public void writeData(DataOutput out) throws IOException { FixStringIO.writeFixString(name, NAME_LENGTH, out); out.writeInt(age); out.writeDouble(salary); FixStringIO.writeFixString(married, MARRIED_LENGTH, out); } //写入一条固定长度的记录到随机读取文件中。 private void writeData(RandomAccessFile out) throws IOException { FixStringIO.writeFixString(name, NAME_LENGTH, out); out.writeInt(age); out.writeDouble(salary); FixStringIO.writeFixString(married, MARRIED_LENGTH, out); } //随机写入一条固定长度的记录到输出流的指定位置。 public void writeData(RandomAccessFile out, int n) throws IOException { out.seek((n - 1) * RECORD_LENGTH); writeData(out); } //从输入流随机读入一条记录，即一个人的数据。 private void readData(RandomAccessFile in) throws IOException { name = FixStringIO.readFixString(NAME_LENGTH, in); age = in.readInt(); salary = in.readDouble(); married = FixStringIO.readFixString(MARRIED_LENGTH, in); } //从输入流随机读入指定位置的记录。 public void readData(RandomAccessFile in, int n) throws IOException { in.seek((n - 1) * RECORD_LENGTH); readData(in); } } //对固定长度字符串从文件读出、写入文件 class FixStringIO { //读取固定长度的Unicode字符串。 public static String readFixString(int size, DataInput in) throws IOException { StringBuffer b = new StringBuffer(size); int i = 0; boolean more = true; while (more && i < size) { char ch = in.readChar(); i++; if (ch == 0) more = false; else b.append(ch); } //跳过剩余的字节。 in.skipBytes(2 * (size - i)); return b.toString(); } //写入固定长度的Unicode字符串。 public static void writeFixString(String s, int size, DataOutput out) throws IOException { int i; for (i = 0; i < size; i++) { char ch = 0; if (i < s.length()) ch = s.charAt(i); out.writeChar(ch); } } }